NimH or Nicad

A year after changing from NiCd to NiMH,I have found that the NiMH are far better and more tolerant of misuse,and have witnessed no evidence of memory effect(early days though),this is using them in radios(TX/RX),remotes,various motor devices,bike lights,torches and telephone.
With NiCds I had to impose a fairly rigorous charging regime with numbers on cells, discharging, etc.With NiMH I haven't bothered and so far no appreciable drop in performance is detectable.
The all out to nothing is a bit alarming at first but you get used to it.
Only disadvantage is that in powering radios and CDs the volume on speakers is lower,a small problem for the aurally challenged like what I am.
They are also cheap!
 
If you regard my posts as BS Cliff then I can only assume that you do not know what you are talking about. Complete dismissal in four letter words generally indicates that and demeans the person doing the dismissing.

I have respect for the knowledge in many of your posts, especially some of the ones regarding metallurgy, and do not lightly dismiss what you say.

But I can only assume that you, unlike many other posters, do not understand that my comments on technical issues are always soundly based and not made lightly. Maybe you just do not like cats?

What I have said regarding the batteries is based on expert technical knowlege that I have access to and which I respect. It is not shallow popular myth and does not come from the literature or views of amateurs or pseudo experts. I have also found it to be correct - for example, I have never had any of the problems others seem to experience with various battery chemistries. Perhaps there is a reason that is so?

John
 
NiMH for me every time! A few years ago I replaced the NiCd batteries in my hand held with NiMH and it is so much better. I hardly ever run it flat and can top it up before each trip. I haven't noticed any memory efect on this or any of the other NiMH batteries I use (camera etc).
 
Both NiCd's and NiMH can both suffer from loss of capacity from crystallisation of the nickel electrode. As said, the problem is rare and if occurs is easily remedied. In the past with NiMH they had a life, in terms of charge/discharge cycles of about half that of NiCd's but a capacity (per weight of battery) of twice that of NiCd's. This shorter life (in terms of cycles) meant that the loss of capacity problem appeared even more rarely with NiMH's - they did not go through enough cycles before failing for other reasons. In terms of capacity delivered from the battery over their lives both chemistries delivered about the same.

The battery manufacturers now seem to give around the same life in cycles to both NiCd's and NiMH's (typically 500 cycles, and the same for Li-ion so are probably being conservative) but from what I have seen those are conservative compared to the life many seem to routinely get, especially for NiCd's which I expect will still give a longer life in cycles (but not necessarily deliver more capacity over that life). So, NiMH now probably delivers more capacity over its life than NiCd's but I have not seen any tests showing this to be so.

Both battery chemistries behave very similarly with respect to charge and discharge except that NiCd's can deliver much higher currents for their size during discharge so remain well suited to high current demand applications (as I said earlier, radio tranmitters). I assume, but do not know, that this carries over to larger batteries and is why we do not see NiMH replacing NiCd's for large battery applications.

Cliff is incorrect when he dismisses my comment about both types suffering the same problems during discharge and charge. This is what Panasonic, for example, have to say for NiMH As with Ni-Cd batteries, repeated charge and discharge of these batteries under high discharge cut-off voltage conditions (more than 1.1V per cell) causes a drop in the discharge voltage (which is sometimes accompanied by a simultaneous drop in capacity). The discharge characteristics can be restored by charge and discharge to a discharge end voltage of down to 1.0V per cell.. They are referring to voltage depression and note that they say it only [/i]sometimes[/i] results in loss of capacity. They also say it is reversible.

Note also that they say to discharge the battery to 1 volt per cell if the problem occurs. If you look at the discharge characteristics of both battery chemistries you will see that this is difficult to manage and the risk is that one can easily drive cells in a battery into reverse charge by over discharging and damaging them.

The greatest enemy of both NiCd's and NiMH is incorrect charging and discharge - this is where almost all the problems people have arise from (ie not from "memory"). In the case of discharge it is the risk of driving cells into reverse charge and, unfortunately, the common myth is that you should manage NiCd's by always running them to dead (or close to it which increases the likelihood of over-discharge) before recharging, that to avoid the dreaded "memory" effect. So more NiCd's die of discharge abuse than do NiMH's, as NiMH's are saved by the other myth that they do not suffer the same effects as NiCd's so do not have to be deeply discharged before recharge. So, a very strange world we live in and Colmce's experience of problems with NiCd's through imposing a fairly rigorous charging regime with numbers on cells, discharging, etc was typical of the difficulties experienced to be expected from the misinformation that prevails in many minds /forums/images/graemlins/crazy.gif.

With respect to overcharging, in my experience modern batteries of both chemistries seem to be very rugged but no doubt rapid charging practices, overcharging, etc do shorten life - again, the battery manufacturers have alot of information of this (and there is plenty of other professional literature relating to the design of high quality chargers).

Note, as some seem to be leaping to vigorous defense of NiMH, that I am not promoting NiCd's over other chemistries and agree for many common applications NiMH is the best choice. But it happens, that some of us have NiCd's still going strong in service after many years, perhaps even before NiMH became available. In some applications NiCd is superior so should not be dismissed out of hand as some seem to do. There is also Li-ion to consider, but which introduces a whole set of its own problems such as short shelf life (20% capacity loss per year seems to be quoted regardless of whether the battery is used or not), usually only available in battery packs incorporating protection circuitry, etc.

No doubt the above will be dismissed as BS by some, but perhaps it will be seen to be of use to those having more open minds and result in them getting longer life from their batteries regardless of their chemistry.

John
 
We ar not talking laboratory control or super high tech chargers - we are talking of what happens in the real world so yes I do dismiss your comments as BS - You frequently make emphatic statements on these forums only to have to waste time trying to defend them - get real and come down out of your ivory tower. There are so many posters who have confirmed their experiences on the matter and their choice of NiMH due to the reduced memory effect and service life.
QED
----------
hammer.thumb.gif
"Artificial intelligence is no match for natural stupidity"
 
Instead of getting angsted about it Cliff, why not look upon it as further explanation, not as defense as you seem to regard it. Of course, in the end, if you don't like it you, just as for anyone else, do not have to read it. But if you do read it, perhaps you could read it properly -

You refer to We are not talking laboratory control or super high tech chargers - we are talking of what happens in the real world .

If you read my post you will see that I am not talking in that laboratory world at all but am talking in the world available to everyone. What I said (not in such brief terms as what follows) is that one should not follow the rigorous regimes promoted by many of controlled deep discharge and then recharge. I said that most damage occurs to the batteries because people (in the real world) do try to follow such controlled regimes running the risk of running the cells into reverse charge. I also said, that if by such a less disciplined approach one does strike difficulties then it is easily reversed.

John
 
Sorry but a Battery Manufacturers Lab is what I believe ...

Mallory Duracell Factory in Sussex ..... highll skilled technician doing research and development of battery technology including rechargeable ....

He stated clearly and with complete 100% faith based on lab experience - HIS - that NiCD are subject to capacity loss due to incomplete discharge and repeated recharge regime - the 'dreaded memory-effect' He confirmed outright that for example :

Full charged NiCD discharged 20%, recharged and repeated resulted in a NiCD capable of only delivering around 20% of its original capacity. This took time to develop - but was a proven fact shown under lab conditions.
NiMH were not prone to the same effect again shown by his lab experience.

The above was all to do with Model flying that we both engaged in and protection of our money and work that had gone into some very nice, expensive models relying on rechargeable battery systems in the flight packs and controllers. A number of modellers had experienced crashes / loss of control of models from failures of cells. He kindly provided service to help us ... he was a modeller himself.

Ships cat ........ your text is similar on all NiCD / NiMH posts and really your wording skates through similar without actually admitting that capacity loss occurs through a NiCD "remembering" its repeated partial discharge ..... whether it is due to crystalization .... which Mallory guy confirmed .... or other - who cares when effect is there. The loss of capacity is the important bit.
He also confirmed the dire practice of shorting a 'dud' cell with a full charged one to kick the dud back to life. But normally results in a cell that has reduced capacity, causes venting of elctrolyte in gas form, and short return to life. How thius works so he explained is that the shorting is destructive of the crystals formed .....

ALL the above I have experienced then, later and still now .... and therefore stopped using NiCD's wherever possible.

Finally the rapid discharge etc. of NiCD's will of course help to keep them healthy .... as the crystals etc. do not have chance to form etc. The cell is discharged heavily and only starts recharge when cell is on that point of significant voltage drop ... near flat !!

So again I disagree partly and also having read again and again your essays on NiCD's etc. say that you are agreeing - but changing words and text to say you don't ... you arrive at similar to others but by different supposed route .... !!
 
Re: Sorry but a Battery Manufacturers Lab is what I believe ...

Hi Nigel

I may be mistaken but I think the only thing difference between us (taking into account what has been in other threads) is that I say the effect (whatever one wishes to call it) is rare and most failures are due to other reasons. I also say that should it occur then it is reversible (which is definitely claimed by battery manufacturers to be so) so one should not run the risk of deep discharging the battery unless the effect displays itself, but not sure if we are in agreement or not on that bit.

I think the difficulty that Cliff has is my claim that NiCd's and NiMH's both suffer from the same effect (whatever one may call it) and that was the main cause of disruption. However, I note that in his post which he has cut and pasted some information from some source, that does, in fact, also say that NiMH's suffer from the same thing but goes on to say "but are less prone to it". The historic reason for that comment is, as I said in my earlier post, NiMH's did not live through enough cycles for the effect to be encountered to the extent found in NiCd's (NiCd's generally living for many more charge cycles).

So, I think if Cliff thinks about what I have said and takes your comments into account (as we have, errr, crossed swords on this before) then he may find that what is being said is not misrepresentative.

Thanks for your balanced response.

{Edit: I do take on board your comment regarding the Mallory technician's comments on NiMH not being subject to the effect. But it does come to mind that Mallory is now Panasonic/Duracell and Panasonic very clearly state in their current technical literature for their NiMh cells that they may be subject to it (will come up in the link I previously gave). Duracell also make the same point.

Perhaps it is again a matter of the historic shorter number of charge cycles that I mentioned, with longer lived (in terms of cycles) NiMH's it is now recognised}.

John
 
Re: Sorry but a Battery Manufacturers Lab is what I believe ...

Huh?

"There is also Li-ion to consider, but which introduces a whole set of its own problems such as short shelf life (20% capacity loss per year seems to be quoted regardless of whether the battery is used or not)"

That's a bit odd! My laptop's Lithium ion battery is 6 years old now and still gives me about an hour and a half under normal operating conditions! The one before it was nearly 10 years old and used to self-discharge pretty rapidly (in a day or so) but if used from fully charged would give at least an hour!
 
Re: Sorry but a Battery Manufacturers Lab is what I believe ...

Read my post properly - I said, shelf life, not operating life as you are talking about" /forums/images/graemlins/frown.gif and the % I gave I qualified by "seems to be quoted" and is said to apply even if the battery is used and then put out of service - and I must emphasise that I have not experienced it either but I always buy fresh batteries regardless so there is no likelihood that I would have and I have no used ones sitting around on the shelf that have been put out of service.

Shelf life problems seem to be a common view and fits in with some of the operating advice from the manufacturers. That advice always is along the lines that it is best to only shallow discharge them and even keep them on charge when not in use. There is also the recommendation that if not used they should still be regularly charged to prevent deep discharge. Obviously, none of those recommendations can be applied to a battery that has sat in a warehouse or slow turnover store for a couple of years. Obviously those recommendations can be adhered to when the battery is in use, so is not then an issue as you have found.

In the end, buying fresh batteries is always good advice and is a habit that has no possible downside whatsoever, so what is the panic about?

But Li-ion does have other inconveniences not least of which is that they are usually only easily available in battery packs, rather than as individual cells, due to the need for charge protection circuitry.

And, everyone, please note that I am not knocking Li-ion so no panicing /forums/images/graemlins/smile.gif. I use them, NiMH's and NiCd's and, unlike some, I do not have any hangups over any of them. They all have their place and I have no particular need to defend any of them over another.

(That will have the sharks biting, I guess?)

John
 
Re: Sorry but a Battery Manufacturers Lab is what I believe ...

Don't worry mate! I CAN read!

It's the "seems to be quoted" bit I was having a dig at!

especially combined with the...

"And, everyone, please note that I am not knocking Li-ion so no panicing . I use them, NiMH's and NiCd's and, unlike some, I do not have any hangups over any of them. " bit!

Just to put your mind at rest, I'm not panicking and I never had any hangups about them either! I just wanted to reassure any anxious people about to hurl themselves off a cliff that in reality, there doesn't seem to be quite as much of a problem with Li-ion batteries as your previous post might have suggested!
 
Re: Cheapest!

No he doesn't even the most rudimentary trawl will reveal cheaper ones,and as they are all made in the same few factories it doesn't matter who you buy them from.
 
You must log in or register to reply here.

Share this page

Top